1. Field
The invention relates to an electronic graphic system.
2. Description of the Related Art
Electronic graphic or image systems in which the painting or drawing of a colour image can be simulated, or a portion of one image can be merged into another by electronic means are well known. One such graphic system is described in our British patent number 2,089,625 and corresponding U.S. Pat. No. 4,514,818, the teachings of which are incorporated herein by reference. This system includes a user operable input device which may be used by the user to select from a range of colours and a range of intensities and to choose from a set of notional drawing implements for use in the painting or drawing.
When a colour is chosen by the user, values representing the components of the selected colour are stored in a colour register. An implement is chosen by selecting from among different implement representations displayed on a display screen and the selected implement is defined by parameters conforming to a 3-dimensional surface representing the profile of the implement. Generally speaking the implement profile will have a high centre falling away to a lower value toward the periphery of the profile although other profiles may, of course, be defined. The implement profile represents the notional distribution of colour which would be applied by the implement to the image over the area of the image which it covers.
The user operable input device is preferably a touch tablet and stylus combination. The touch tablet is arranged to generate position signals designating the position of the stylus relative to the touch tablet when the stylus is brought into proximity. When the stylus is applied to the touch tablet a pressure signal representing the pressure applied via the stylus to the touch tablet is output from the stylus and stored in a pressure signal register. For some implements, representing say paint brushes, position signals are allowed to be generated for each movement of the stylus by the distance between picture points or similar distance, whilst for other implements, say air brushes, position signals are generated at regular time intervals, even if the stylus is held stationary on the touch tablet.
When a position signal is produced, new video signals (pixels) are derived for every picture point in the patch covered by the selected implement. An image store is provided and each new pixel is written at the appropriate picture point in the store. Such new pixels are derived by a processing circuit in accordance with the selected colour data and the distribution of the selected implement, and in response also to the pressure applied to the stylus and to the value of the pixel previously stored at the respective picture point in the store.
The user, who it is envisaged would normally be an artist lacking experience in the use of computer based systems, paints or draws by choosing a desire colour and implement and then manipulating the stylus, causing the touch tablet to generate a series of position signals which define the path or positioning of the stylus. The processing circuit reads pixels from the image store for a patch of picture points in response to each position signal and these pixels are blended by the processor with signals representing the chosen colour in proportions depending upon the respective values of the brush profile and pressure. The blend is then written back to the picture store replacing the pixels previously stored therein.
In general, the blending process is carried out a number of times for each picture point in the image store whether the implement is moving or stationary (assuming in the case of the moving implement that the patch covered by the implement is larger than the spacing between picture points). The final proportion will depend on the number of processing operations performed per pixel.
To enable the user to observe his creation, the stored picture is read repeatedly and the pixels are applied to a TV-type colour monitor, so that the build-up of the picture can be observed. Of course such systems are not limited to TV-type formats and any suitable video format may be adopted. The system described avoids the problem of jagged edges in the image, an unpleasant stepping appearance normally associated with lines not lying horizontally or vertically in a raster display.
Another system which enables a user to perform picture composition in addition to painting is described in our British Patent No. 2113950 and corresponding U.S. Pat. No. 4,602,286, the teachings of which are also incorporated herein. In this system stores are provided for storing data representing two independent pictures and a control image or stencil. A stencil is produced for example by xe2x80x9cdrawingxe2x80x9d data into the control image store. The stencil data is used to control the combining of the data representing the two independent pictures to produce data representing a composite picture. The data representing the composite picture is output continuously for display of the picture on a monitor. Once the user is satisfied with the displayed composite picture the composite data is stored permanently for subsequent processing or printing for example.
According to one aspect of the invention there is provided an electronic graphic system comprising: an image store for storing data defining a multiplicity of picture elements that together form an image; user operable means for generating position data representing a sequence of positions including a first position; a brush store for storing data defining a drawing implement as a patch of brush data; and a processor for processing data in the store by reading patches of initial image data from the store at locations related to the position represented by the position data, determining an image value as the value of a predetermined pixel in a patch of data at a location corresponding to the first position, modifying image data in patches read from the store with the determined image value depending on the patch of brush data and writing each patch of modified data back to the store so as to replace the respective patch of initial data previously stored therein.
According to another aspect of the invention there is provided a method of processing image data, the method comprising: storing data defining a multiplicity of picture elements that together form an image; generating position data representing a sequence of positions including a first position; storing data defining a drawing implement as a patch of brush data; and processing data in the store by reading patches of initial image data from the store at locations related to the positions represented by the position data, determining an image value as the value of a predetermined pixel in a patch of data at a location corresponding to the first position, modifying image data in patches from the stored data with determined image value depending on the patch of brush data and writing the patch of modified data back to the stored data so as to replace the patch of previously stored initial data.
The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an exemplary embodiment of the invention given with reference to the accompanying drawings.